Another week, another resignation. Today it was the turn of Lady Buscombe, the chair of the Press Complaints Commission, to step down from her role overseeing self-regulation of newspapers. This departure had an air of inevitability about it. The November 2009 PCC report into phone hacking was a risible document which was almost wilfully blind in its inability to see the significance of publicly available evidence or to ask searching questions of the appropriate people. Earlier this month the PCC withdrew that report, belatedly accepting the obvious: that it had gullibly accepted the News International "one rotten apple" explanation of behaviour at the News of the World. But by then the damage had been done. It was apparent then – and has become even more so since – that the PCC is not a "regulator" in any accepted sense of the word. It has no effective ability to investigate or to apply meaningful sanctions. The 2009 report was, as we warned at the time, "dangerous to the press" because it would call into question the credibility of self-regulation itself. Thus it has proved.

The PCC is now advertising for a new chair to step into Lady Buscombe's shoes. Since it is unlikely that the PCC will survive the inevitable scrutiny of Lord Leveson's forthcoming inquiry this is, on the face of it, not the most attractive job in the world. But the PCC does serve a useful role as a mediator and its code of practice remains a good set of practical and ethical guidelines. So it is right that the PCC continues its work while the industry, and others, decide on the regulatory framework which will replace the PCC.

At the end of a week in which Lord Leveson put more flesh on the bones of how he intends to proceed this autumn, there remain some very troubling questions about how Andy Coulson came to be appointed to his role at No 10; what sort of vetting was involved; and what access he had to sensitive information, given his relatively low security clearance.

People in line for highly sensitive jobs are vetted to find out anything compromising which could make them vulnerable to blackmail or other forms of undesirable influence. Given the criminal cases and press coverage relating to Coulson's period as editor of the NoW, David Cameron's determination to bring him to Downing Street looks extremely puzzling. Why was he not put through the sort of routine vetting procedures to which his predecessors and successor were subjected? Which ministers or officials approved the decision to give him only a cursory security check? Given his lack of clearance, what information did he have access to and which sensitive meetings did he attend? We now know that News International had evidence in 2007 that Coulson had knowledge of illegal payments to police officers. Did that report have the potential to make him vulnerable to external pressure?

These are important questions – and we hope that Lord Leveson will see it as his duty to ask them, for otherwise this will remain an unexamined aspect of this affair. The prime minister has, with some justification, boasted of his commitment to transparency over his relationship with powerful media figures. But on this issue he is curiously coy. More worrying is the refusal of public servants to come clean about the questions – including Sir Gus O'Donnell, the cabinet secretary, Jeremy Heywood, the Downing Street permanent secretary, and Craig Oliver, the current head of communications. The series of questions posed by the Guardian to Downing Street this week are relatively straightforward and could, in the spirit of openness, be answered perfectly simply. It is not the role of public officials to deflect, or block, awkward questions or to protect politicians from embarrassment. Nor should these same officials attempt to limit the terms of reference under which Lord Leveson could, and should, consider these issues at the heart of government.